The present invention relates to a polygon mirror motor and a polygon mirror supporting structure; and, more particularly, to a polygon mirror motor suitable for use, for example, in a laser beam printer or a light write-in apparatus of an image forming apparatus, and to a polygon mirror installation supporting structure of a polygon mirror apparatus.
A polygon mirror motor is generally found in a laser beam printer and a laser beam scanning apparatus of an image forming apparatus. This polygon mirror motor carries a polygon mirror fixed to a rotative shaft of a brushless motor, and such a polygon mirror provides a mirror surface on the side of a member which is formed in a regular polygon shape, such as a six angle regular shape or an eight angle regular shape.
A laser light beam irradiates the rotating polygon mirror portion, which reflects the light onto a photosensitive body, causing it be scanned thereby, so that a light write-in operation is carried out. In such a polygon mirror motor structure, to perform an accurate scanning operation, it is necessary to maintain a right angle between the rotative shaft and the polygon mirror, which often becomes a problem. To avoid this problem, the method used for fixing the mirror to the rotative shaft, or to a flange portion which is fixed to the rotative shaft, becomes important.
As conventional mirror securing methods, there are various techniques which are described in Japanese patent laid-open publication No. Sho 62-80,616, Japanese patent laid-open publication No. Sho 61-175,612, Japanese utility model laid-open publication No. Hei 3-45,073, Japanese utility model laid-open publication No. Hei 2-134,513, Japanese utility model laid-open publication No. Hei 2-64,915, Japanese utility model laid-open publication No. Sho 6432,513 and Japanese utility model laid-open publication No. Sho 63-198,022.
As proposed in the above stated various prior techniques, the mirror is installed against a face of a rotating member supporting body, which is fixed to the rotative shaft using a screw member securing method, a spring member pressing method, an adhering method, an elastic body interposition method or a wedge securing method, etc.
However, in the screw member securing method, according to the conventional technique, during the screw member fastening operation, a variation in the fastening torque due to a variation of the component accuracy resulting from manufacturing tolerances at each of screw member portion is unavoidable. Further, since screw members and metal washers are necessary, the number of components increases, and since a tap hole processing for providing a hole in the supporting member for the mirror is necessary, the manufacturing process is complicated and the component accuracy is inferior.
In the spring member pressing method, according to the conventional technique, the defects of the screw member fixing method are avoided, however the pressure force applied to the mirror changes according to a variation of the spring constant of the spring member. Namely, when the pressure force applied to the mirror is weak, the mirror moves, and when the pressure force applied to the mirror is strong, the mirror will deform.
In the adhering method, according to the conventional technique, an unbalance is generated due to a non-uniformity in the amount of applied coating and a dispersion of non-hardened liquid. Further, the mirror deforms in response to heat generated during the high speed rotation of the polygon mirror motor, and this causes an unbalance.
In the elastic member interposing method, according to the conventional technique, the elastic member tends to creep due to thermal stress, and the pressure force provided via the elastic member becomes weak, thus the mirror moves.
In the above stated mirror securing methods, including the wedge securing method, components in addition to the mirror and the mirror installation metal seats are necessary, so that the assembly including the polygon mirror motor has a high cost.
The problems in the various conventional techniques for securing the polygon mirror to the rotating member supporting body make it difficult to accurately maintain the mirror face in a regular polygon shape. To maintain the accuracy of the mirror face and to prevent a deformation thereof, between the rotating member supporting body and the mirror, other components are interposed, so that a high processing cost and high component costs are necessary.
Further, since many components, in addition to the rotating member supporting body and the mirror, are used and fixed to the motor shaft, an unbalance is generated due to a mass difference between different portions of the assembly, and this causes a vibration during high speed rotation. Also, with a construction having the above stated components, a change in the components with time due to high speed rotation is unavoidable, thereby the life of the polygon mirror motor is remarkably shortened.
The above stated conventional techniques for fixing the rotating member supporting body to the regular polygon shape mirror, which is opposed to and in contact with the rotating member supporting body, have serious inconveniences. The problems to be solved to eliminate the inconveniences in the conventional techniques reside in the need to establish a predetermined accuracy of the mirror face, the increase in a number of the components, the increase in unbalance due to the variations resulting from manufacturing tolerances of the components, a regeneration in unbalance due to a change in the components with time, the increase in the regeneration in unbalance due to changes which occur over time, the shortening in the life of the assembly due to vibration and a lowering in performance by unstable reflection of the laser beam light due to distortion of the mirror face.